Method and system for backing up data of data processing devices including fixed length block format data conversion to variable length block format

ABSTRACT

In a computer system that includes a first computer, a second computer, a first storage apparatus storing data in a fixed-length block format used by the second computer, and a backup apparatus connected to the first computer and storing data in a variable-length block format, the present invention provides a backup method for backing up data stored in the first storage apparatus to the backup apparatus. The first computer sends the second computer a request to read data in the fixed-length block format. In response to this request, the second computer reads the fixed-length block format data from the first storage apparatus and transfers this data to the first computer. The first computer converts the transferred fixed-length block format data into variable-length block format data. The converted variable-length block format data is stored in the backup apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No.08/912,872 filed Aug. 19, 1997, now U.S. Pat. No. 6,115,797, the subjectmatter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for backing up and restoringdata stored in storage apparatuses in computer systems.

Disk arrays are generally used as storage apparatuses in computersystems to provide high performance and a high degree of reliability. In“open systems” such as work stations and personal computers (PCs),fixed-length block formats are used as the format with which to recorddata to external storage apparatuses such as disk storage apparatuses.Thus, fixed-length access interfaces are generally used in theinterfaces between the open systems and disk array controllers.Fixed-length access interfaces are also used for the individual diskstorage apparatuses within a disk array.

In general-purpose large-scale computers (hereinafter referred to asmainframes), variable-length block formats are used to record data tomagnetic disk storage apparatuses. For this reason magnetic disk storageapparatuses are accessed using variable-length access interfaces, e.g.,CKD (Count Key Data), that allow access to variable-length block formatdata. Conventionally, data in variable-length block formats has beenphysically recorded on disk storage apparatuses having variable-lengthaccess interfaces. However, in recent years there has been widespreaduse of disk arrays, formed from relatively inexpensive disk storageapparatuses used in PCs and workstations, as storage apparatuses for therecording of data using variable-length block formats.

In mainframe disk arrays, data is generally recorded to individual diskstorage apparatuses using a fixed-length block format known as FBA(Fixed Block Architecture), as can be seen in “Mainframe '98” (Nikkei BPCorp., pp. 126-130). Disk array controllers are equipped with aconversion function that uses cache memory to convert betweenfixed-length block formats and variable-length block formats. Mainframesand disk controllers are connected using a variable-length accessinterface. Read/write requests from a mainframe are formed from aplurality of input/output commands known as CCWs (Channel CommandWords). This plurality of CCWs is known as a CCW chain. CCW chains arecreated by the mainframe's operating system in response to requests fromapplications.

Magnetic disk storage apparatuses are generally installed external to amainframe as a disk subsystem formed from a disk controller and a diskstorage apparatus. To read or write data to the disk storage apparatus,the mainframe sends the disk subsystem using a command based on avariable-length block format. The disk controller in the disk subsystemreceives the command specified by the mainframe and converts the datafrom the variable-length block format to a fixed-length block format inorder to allow access to the disk storage apparatus. This type ofconversion from variable-length format to fixed-length format isdescribed, for example, in Japanese laid-open patent publication numberHei 6-150557.

Computer centers today often include both mainframes and open systems.In such settings, there has been a need to allow easy management of diskarrays by storing the data accessed by the mainframes and the opensystems together, thus centralizing the disk array. A technology thatmeets this need is described in page 145 or page 151 of “Mainframe '98”(Nikkei BP Corp.), where an open system can access mainframe data storedin a disk array equipped with both a variable-length access interfaceand a fixed-length access interface. For the mainframe data,variable-length/fixed-length block format conversion is performed withinthe disk array, and the data is stored in a disk storage apparatus usingthe fixed-length block format. The mainframe data stored in the diskstorage apparatus is retrieved by an open-system server via thefixed-length block format interface. The data is retrieved in the sameform as it is stored on the disk storage apparatus. Furthermore, byusing a backup/restore option on the mainframe, a volume in the diskarray for use by an open system can be read by the mainframe as a volumeimage and backed up. Also, the mainframe can restore the backed up datato the volume for use by the open system. Use of this feature does notrequire installation of special software on the mainframe or the opensystem. To allow the fixed-length block format data from the open-systemvolume to be accessed by the mainframe, the disk array controllerconverts the data to the variable-length block format. The backupdestination can be an existing tape library apparatus, magnetic tape,disks, etc. When an open-system volume in the disk array is initialized,a volume serial number and volume information is created for the volume.The volume serial number and the volume information written to thevolume during initialization is written to an area separate from thearea in which the open-system data is written. Thus, the open-systemdata is not destroyed. Data stored in other disk storage apparatusesconnected to the server connected to the disk array as well as datastored in disk storage apparatuses connected to other servers/clients onthe network are backed up using backup programs or system commands onthe open systems. The data is backed up in backup/restore volumes in thedisk array. Volume information and volume serial numbers are created forthe backup/restore volumes during initialization. Data that has beenbacked up to a backup/restore volume can, as described above, then bebacked up to a tape library apparatus or the like using the mainframe'sbackup feature.

There has also been the emergence of the use of SCSI interfaces, whichare fixed-length access interfaces, as the interface for externalstorage apparatuses used for general-purpose data processing devices.For example, in pp. 53-54 of “Mainframe '98” (Nikkei BP Corp.), aninternal disk storage apparatus is described where a disk storageapparatus that uses a fixed-length block format is mounted inside thecase of a data processing device. A set of commands (CCW) forreading/writing data using the variable-length block format generated bythe operating system is interpreted by a processor, referred to as anSAP, which converts these commands to a set of commands (SCSI commands)for reading/writing data using the fixed-length block format, andinput/output operations are performed on the internal disk. In the datastored in the internal disk storage apparatus, data in thevariable-length block format is embedded in fixed-length block formatdata. This conversion of data formats is performed by the SAP.

SUMMARY OF THE INVENTION

With the conventional technology described above, taking data from anexternal storage apparatus shared by open systems and mainframes andhaving the open system back the data up to a mainframe's backup storagerequires the data to be copied to a backup volume in the externalstorage apparatus shared with the mainframe. Thus, each time a backup isto be made, a backup volume must be created. This means that a singlebackup requires two backup operations. This requires allocation ofstorage capacity and backup processing.

The object of the present invention is to reduce the size of the backupvolumes used in backup operations and to provide a method for performingbackups that reduces the overhead involved in backup operations. Inorder to achieve the objects described above, the first form of thepresent invention is described as follows. In a computer system thatincludes a first computer, a second computer, a first storage apparatusstoring data in a fixed-length block format used by the second computer,and a backup apparatus connected to the first computer and storing datain a variable-length block format, a backup method for backing up datastored in the first storage apparatus to the backup apparatus isprovided. The first computer sends the second computer a request to readdata in the fixed-length block format. In response to this request, thesecond computer reads the fixed-length block format data from the firststorage apparatus and transfers this data to the first computer. Thefirst computer converts the transferred fixed-length block format datainto variable-length block format data. The converted variable-lengthblock format data is stored in the backup apparatus. The second form ofthe present invention is described as follows. In a computer system thatincludes a first computer, a second computer, a storage apparatusstoring data in a fixed-length block format used by the second computer,and a backup apparatus connected to said first computer and storing datain a variable-length block format, a backup method for backing up datastored in the first storage apparatus to the backup apparatus isprovided. Volume information used to allow the first computer to accessfixed-length block format data is stored in a region distinct from aregion in which the fixed-length block format data is stored. Based oninformation contained in the volume information, the first computerreads the fixed-length block format data from the storage apparatus. Inthe first computer, the fixed-length block format data is converted tovariable-length block format data. The first computer takes the dataconverted to the variable-length block format and stores it in thebackup apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a computer system according to anembodiment of the present invention.

FIG. 2 is a schematic diagram showing the logical structure of anopen-system volume.

FIG. 3 is a schematic diagram showing the track format used in avariable-length block format.

FIG. 4 is a schematic diagram showing the track format used in afixed-length block format.

FIG. 5 is a drawing for the purpose of describing the conversion of datain a variable-length block format to data in a fixed-length blockformat.

FIG. 6 is a flowchart of the operations performed during a backup of amainframe volume.

FIG. 7 is a flowchart of the operations performed during a backup of anopen-system volume.

FIG. 8 is a flowchart of the operations performed during a backup of anexternal storage apparatus used exclusively by an open system.

FIG. 9 is a flowchart from another embodiment showing the operationsperformed during a backup of data stored in an external storageapparatus used exclusively by an open system.

FIG. 10 is a block diagram showing the architecture of a computer systemaccording to yet another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram of a computer system according to anembodiment of the present invention. A mainframe 1 includes: at leastone central processing unit (CPU) 12; a main memory 11; communicationunits (I/O channels) 13, 15, 16 for controlling data transfers withother data processing devices; and at least one storage controlprocessor 14. The I/O channel 13 includes a variable-length accessinterface and is connected to a backup apparatus 3 via a communicationline 30. The I/O channel 15 includes a fixed-length access interface andis connected to an external storage apparatus 4 via a communication line31. The fixed-length access interface used between the I/O channel 15and the external storage apparatus 4 can be, for example, a SCSI (SmallComputer System Interface) interface or a fiber channel, formed fromoptical cable, that uses the SCSI protocol. Besides the areas forstoring data and programs used by the CPU 12, the main memory 11includes a cache memory 111 used when data is sent to or received fromthe external storage apparatus 4. The cache memory 111 serves as a diskcache. The storage control processor 14 includes a data format converter141 that provides conversion between the variable-length block formatand the fixed-length block format. In this embodiment, the data formatconverter 141 is implemented as a program that is executed by thestorage control processor 14. The storage control processor 14 controlsdata transfers between the external storage apparatus 4 and the mainmemory 11. Data read from the external storage apparatus 4 and data fromthe CPU 12 to be written to the external storage apparatus 4 is storedin the cache memory 111. The data is stored in the cache memory 111using the same fixed-length block format used by the external storageapparatus 4.

The open system 2 is a server apparatus including: a central processingunit (CPU) 22; a main memory 21; and communication units (I/O channels)23, 24 for controlling data transfers with other data processingdevices. The I/O channel 23 and the I/O channel 13 are variable-lengthaccess interfaces. The mainframe 1 and the open system 2 are connectedby the I/O channel 16 and the I/O channel 24 via a communication line34. The I/O channel 23 includes a fixed-length access interface and isconnected to the external storage apparatus 4 via a communication line32. The I/O channel 23 is also connected to an external storageapparatus 5 via a communication line 33.

The mainframe 1 acts as the server for the external storage apparatus 4.The external storage apparatus 4 stores data using the fixed-lengthblock format and includes a fixed-length access interface. The externalstorage apparatus 4 can be either a single disk storage apparatus or aRAID (Redundant Array of Inexpensive Disks) having a fixed-length accessinterface. The external storage apparatus 4 includes a mainframe volume42 and an open-system volume 43. The mainframe volume 42 is a volume forstoring data from the mainframe 1 and can be accessed only from themainframe 1. The open-system volume 43 is initialized by a volumeinformation creation/data set allocation module 1121 of the mainframesystem 1. In this initialization operation, volume information and avolume serial number are created for the open-system volume 43.

The backup apparatus 3 can be, for example, an MT library apparatus thatuses magnetic tape (MT) as the recording medium. It would also bepossible to use a disk storage apparatus instead of an MT libraryapparatus for the backup apparatus 3.

FIG. 2 is a schematic diagram showing the logical structure of theopen-system volume 43. The open-system volume 43 contains volumeinformation 431 and a volume serial number 433. The volume information431 contains information used to identify the start and end positions ofuser data 432 in the volume 43. The volume serial number 432 is anidentifier assigned to distinguish the volume 43 from other volumes. Thevolume information 431 and the volume serial number 433 are written toan area separate from the area in which the open-system user data 432 iswritten. Thus, the user data 432 for the open system is not destroyed.By creating the volume information 431 and the volume serial number 433,the open-system volume 43 allows access from the mainframe 1. However,only a backup/restore program 112 can be used to access the open-systemvolume 43 from the mainframe 1. The volume information 431 is stored inthe variable-length block format, and the user data for the open-systemis stored in the fixed-length block format. In addition to what isdescribed above, the volume information 431 and the volume serial number433 can also be stored in another volume independent from theopen-system volume 43 or in the cache memory 111 of the mainframe 1.

The volume information and the volume serial number which are needed toback up data from the open-system volume 52 in the external storageapparatus 5 are created in the mainframe 1 or in the external storageapparatus 4. The operating system 113 makes it appear as though thevolume exists in the mainframe 1 or the external storage apparatus 4.Volume serial number identifying means 142 in the storage controlprocessor 14 is used to determine where the actual volume is located.The storage control processor 14 uses the volume serial number to selectan operation based on the storage location. If the volume is in theexternal storage apparatus 4, the backup operation is performed directlyon the volume. If the volume is in the external storage apparatus 5, thedata to be backed up is retrieved via the open system 2 connected to theexternal storage apparatus 5.

FIG. 3 is a schematic diagram showing the track format used in thevariable-length block format. The figure shows a sample structure of asingle track. The track is formed from a single home address(hereinafter abbreviated as HA) 510 and at least one record 500. The HA510 is the first field positioned at the start of each track andcontains information such as the track number. The record 500 includesmultiple fields: a count field 501 and a data field 502. In some cases akey field (not shown in the figure) may be present in front of the datafield 502. The count field 501 is a fixed-length field that containsinformation such as the address of the record 500, the lengths ofsubsequent fields (the data field 502 and the key field), and the like.Each of the records 500 can be a variable-length record. In other words,the length of the data field 502 can be different for each record 500.Thus, the count field 501 stores the length of the key field and thedata field 502 of the record. By looking at the count field 501, thelengths of the fields in the record 500 can be determined. The addressof the record 500 is indicated by a cylinder number, a head number, anda record number, i.e., a number assigned sequentially from the start ofa track. Tracks have fixed lengths but records have variable lengths, sothe number of records contained in each track varies.

FIG. 4 is a schematic diagram showing a track format used in thefixed-length block format. In fixed-length storage apparatuses, eachtrack is formed from regions (hereinafter referred to as blocks) 600having a predetermined fixed length. Each block 600 is assigned a uniquenumber in the storage apparatus. Access to the storage apparatus isperformed using the number of the leading block 600 of a region and thenumber of subsequent blocks 600.

FIG. 5 is a drawing for the purpose of describing the conversion of datain a variable-length block format to data in a fixed-length blockformat. When each track represented in the variable-length block formatis converted, it is split into regions having the same size as thefixed-length blocks 600. The leading region of the leading trackindicated by cylinder number 1 and head number 0 is assigned to theleading block 600 indicated by the number 0. Subsequent regions on thetrack are assigned to subsequent blocks 600. Once all the regions in theleading track have been assigned, the leading region of the next track,i.e., cylinder number 1, head number 1, is assigned to the subsequentblock 600. At this point, the count field 501 of the variable-lengthblock format is discarded rather than saved. In this manner, all regionsof all tracks are associated to the blocks 600. The volume informationis stored in cylinder number 0. If the mainframe volume 42 and theopen-system volume 43 have the same track format in the external storageapparatus 4, the same data format converter 141 can be used for backingup the open-system volume 43 from the mainframe 1 as well as for backingup the mainframe volume 42. Thus, it would be desirable to use the sametrack format for both the mainframe volume 42 and the open-system volume43. Since the open-system data, e.g., SCSI data, does not contain acount field, the track format of the mainframe data is made to conformto the track format of the open-system data. When the mainframe issues aread request, the data format converter 141 of the storage controlprocessor 14 generates a count field. When the mainframe 1 issues awrite request, the count field is discarded and only the data field isstored. Since the tracks have a fixed length, the number of fixed-lengthblocks 600 that can be placed in a single track is determined by thetrack size divided by the block size. The block number of the leadingblock 600 holding a track can be determined from the track address asfollows: “(cylinder number×number of heads+head number)×total number ofblocks in a track”.

For normal use of data in the external storage apparatus 4 by the opensystem 2, the open system 2 reads data directly from the open-systemvolume 43 in the external storage apparatus 4 in response to a readrequest issued from an application program 212. Backups of themain-frame volume 42 and the open-system volume 43 in the externalstorage apparatus 4 are made in the following manner.

FIG. 6 is a flowchart showing the operations performed when themainframe 1 makes a backup of the mainframe volume 42. To back up themainframe volume 42, first the backup software 112 is started (step1001). The backup software 112 reads the backup data from the mainframevolume 42 (step 1002). The data format converter 141 of the storagecontrol processor 14 takes this backup data and converts it from thefixed-length block format to the variable-length block format (step1003). The data that has been converted to the variable-length blockformat is stored in the backup apparatus 3 connected to the mainframe 1(step 1004). The backup software 112 checks to see if there is any moredata to be backed up. If there is, the operations from step 1002 throughstep 1004 are repeated to continue the backup operation. If all the datahas been backed up, the backup operation is finished (step 1005).

As with the backup operation, the restoring of backed up data isperformed by the backup software 112. The backup software 112 uses thedata format converter 141 to take the backup data stored in the backupapparatus 3 and convert it from the variable-length block format to thefixed-length block format. This is then stored in the mainframe volume42.

FIG. 7 is a flowchart showing the operations performed when themainframe 1 backs up the open-system volume 43. In the backup operationfor the open-system volume 43, first all operations on the open system 2that use the volume to be backed up are halted, and the volume 43 isunmounted (step 1301). The backup software 112 of the mainframe 1 isthen started. The backup software 112 receives from the user a volumeserial number corresponding to the device filename of the volume 43 usedby the open system 2 and begins backing up data (step 1302). Then,operations similar to those of step 1002-step 1005 described above areperformed to make the backup (step 1303). Once all the data has beenstored in the backup apparatus 3, the volume 43 is mounted to the opensystem 2 and the open system 2 resumes operations (step 1304).

The restore operation for the open-system volume 43 is performed in asimilar manner as the restore operation for the mainframe describedabove.

FIG. 8 is a flowchart of the operations performed when data from theopen-system volume 52 in the external storage apparatus 5 is backed upto the backup apparatus 3. The data in the volume in the externalstorage apparatus 5 cannot be accessed directly from the mainframe 1 andis first copied to the external storage apparatus 4 before being savedto the backup apparatus 3.

In the backup operation for the open-system volume 52, first a backupvolume is created in the external storage apparatus 43. The volumeinformation creation/data set allocation module 1121 generates a volumeserial number and volume information for the backup volume, and theseare saved in the cache memory 111 or the external storage apparatus 4.The backup volume, the volume serial number, and the volume informationare generated based on user specifications (step 1401). Then, the opensystem 2 uses its backup program or system commands in order to copy thedata to be backed up from the open-system volume 52 to the backup volumein the external storage apparatus 4. This operation is known as atemporary backup. The copying performed here can be performed, forexample, on a file-by-file basis. This involves copying multiple filesthat will fit in the capacity of the backup volume (step 1402). Aftercopying the backup data, the operations being performed by the opensystem 2 are halted and the backup volume is unmounted from the opensystem 2 (step 1403). Next, the backup software 112 of the mainframe 1specifies the backup volume and reads data. The data format converter141 of the storage control processor 14 takes the data read from thebackup volume and converts it from the fixed-length block format to thevariable-length block format while generating a virtual C field (step1404). The data converted into the variable-length block format isstored in the backup apparatus 3 (step 1405). After all the data fromthe files that were temporarily backed up to the backup volume have beenstored in the backup apparatus 3, the files that were copied to thebackup volume are all deleted so that the backup volume can be used asthe temporary backup destination for the next backup (step 1406). Thebackup volume 44 is mounted to the open system 2, allowing the backupvolume to be accessed from the open system 2 (step 1407). The volume 52is checked to see if there is data that needs to be backed up. If thereis data remaining to be backed up, the operations starting with step1402 are repeated. If there is no more data to be backed up in thevolume 52, the backup operation is finished (step 1408).

To restore the backed up data, the data is converted from thevariable-length block format to the fixed-length block format. The datais then passed on to the open system 2 via the backup volume and issaved in the open-system volume 52.

FIG. 9 is a flowchart showing the operations performed in a backupoperation according to a second embodiment where data from theopen-system volume 52 of the external storage apparatus 5 is backed upto the backup apparatus 3. In the operation shown in FIG. 9, the storagecontrol processor 14 makes a backup using the volume information 431 todetermine the storage location of the backup data. In this embodiment,the volume information associated with the backup data is created in thecache memory 111.

In the backup operation for the open-system volume according to thisembodiment, first all operations on the open system 2 that use theopen-system volume 52, which is the volume to be backed up, are stopped.After stopping operations, the open system 2 unmounts the volume 52 (orexecutes a command from the OS using the volume) (step 1101). Next, thevolume information creation/data set allocation module 1121 of thebackup software 112 generates volume information and a volume serialnumber for the external storage apparatus 5 connected to the open system2. These are stored in the cache memory 111 of the main memory 11. Thecache memory 111 is treated as though it contains an imaginary volume.In this example, the volume information is stored in the cache memory111 but it would also be possible to store the volume informationelsewhere. To simplify operations, it would be desirable to have thedevice filename used by the open system 2 associated with the volumeserial number. Also, the volume serial number is assigned by the systemwithin a range of numbers so that the data can be identified asbelonging to the external storage apparatus 5. The volume serial numberis managed and handled by the user (step 1103).

The backup software 112 generates volume information. This volumeinformation is used to request the storage control processor to read thebackup data and begin performing the backup operation (step 1104). Thestorage control processor 14 uses volume serial number identifying means142 to determine if the specified volume serial number is within anumerical range associated with data from the external storage apparatus5. If the specified volume serial number is not within a rangeassociated with data from the external storage apparatus 5, theopen-system volume in the external storage apparatus 4 is backed up.Thus, in this case operations similar to the one at step 1303 areperformed (step 1105). If the specified volume serial number is withinthe range associated with data from the external storage apparatus 5,the storage control processor 14 uses the communication line 34 torequest the open system 2 to read data. In response to this request, theopen system 2 starts a backup program and reads backup data from theopen-system volume. This data is transferred via the communication line34 to the storage control processor 14 (step 1106). The storage controlprocessor 14 uses the data format converter 141 to convert the datatransferred from the open system 2 into the variable-length block formatwhile generating virtual C fields (step 1107). This allows the data tobe used by the operating system 113 of the mainframe 1. The storagecontrol processor 14 sends the converted data to the operating system113. The data sent to the operating system 113 is stored in the backupapparatus 3 by the backup software 112 (step 1108). The storage controlprocessor 14 then checks to see if there is any remaining backup datafrom the open system 2. If there is backup data remaining, theoperations from step 1107 through step 1108 are repeated (step 1109).Once all the backup data has been processed, the storage controlprocessor 14 reports that the backup operation has been completed. Theopen system 2 mounts the open-system volume 53 and resumes operations(step 1110).

Another method is to backup data after a certain amount of data has beencollected from the open system 2.

To restore a backup, the backup software 112 reads the backup datastored in the backup apparatus 3 and uses the data format converter 141to convert the data to the fixed-length block format. The storagecontrol processor 14 transfers the data converted to the fixed-lengthblock format to the open system 2 via the communication line 34. Theopen system 2 restores this data to the open-system volume 52.

In the embodiment described above, data stored in the external storageapparatus 5, which is used exclusively by the open system 2, is backedup by going through the open system 2. Instead of the method describedabove, it would also be possible to have the communication unit 15 ofthe mainframe 1 connected to the communication unit 35 of the externalstorage apparatus 5 so that data can be backed up without going throughthe open system 2. In this case, a backup software 112 would prepare forthe backup beforehand by generating a volume serial number and volumeinformation for the external storage apparatus 5 (the open-system volume52), which would then be stored in the cache memory 111. The backupoperation could then be performed in a manner similar to the backup ofthe open-system volume 43 indicated by the flowchart in FIG. 7. In orderto prevent access errors with the external storage apparatus 5,mainframe 1 would keep the external storage apparatus 5 unmounted or thecommunication line 35 off-line at most times. Then, when the backupsoftware 112 is started, the mainframe 1 would make the external storageapparatus 5 accessible.

FIG. 10 is a block diagram showing the architecture of a computer systemaccording to yet another embodiment of the present invention. In thecomputer system according to this embodiment, an external storageapparatus network 6 connects: a mainframe 1; an open system 2; a backupapparatus 3; and external storage apparatuses 4, 5. The external storageapparatus network 6 is connected to the different elements bycommunication lines 34, 35, 36, 37, and 38. The mainframe 1, the opensystem 2, and the external storage apparatuses 4, 5 includecommunication units 17, 25, 45, and 55 respectively in order tocommunicate with other devices via the external storage apparatusnetwork 6. Under normal conditions, the external storage apparatus 4 canbe accessed from the mainframe 1, and the external storage apparatuses4, 5 can be accessed from the open system 2. The cache memory 111 of themainframe 1 holds a volume serial number 114 and volume information 115corresponding to the open-system volume 52 in the external storageapparatus 5. These are generated by the backup software 112 before abackup is performed.

The backup operation in this embodiment is implemented in a similarmanner as the backup operation of the open-system volume 43 describedabove with reference to the flowchart in FIG. 7, except that thetransfer of backup data takes place via the external storage apparatusnetwork 6 between the mainframe 1, the corresponding external storageapparatus, and the backup apparatus 3.

According to the embodiment described above, in a computer system thatincludes both mainframes and open systems, data from disk storageapparatuses or the like connected to and used by open systems can bebacked up to a backup apparatus 166 connected to a mainframe. Also,open-system data can be backed up while data is being retrieved by themainframe. This eliminates the need for the mainframe to create a backupvolume in the external storage apparatus, allowing the backup operationto be performed quickly and eliminating the need to allocate storagecapacity for the backup operation.

The present invention is not restricted to the embodiments describedabove. For example, it is not necessary for there to be only onemainframe and one open system in a single system. Two or more of eachcan be present. Similarly, it would be possible to use any number ofexternal storage apparatuses.

What is claimed is:
 1. In a computer system including: a first computer;a second computer connected to said first computer via a communicationline; a first storage apparatus connected to said first computer; asecond storage apparatus connected to said second computer via afixed-length access interface and storing data in a fixed-length blockformat used by said second computer; and a backup apparatus connected tosaid first computer via a variable length access interface and storingdata in a variable-length block format; a backup method for backing updata stored in said second storage apparatus to said backup apparatuscomprising the steps of: making volume information for accessing datastored in said first or second storage apparatus from said firstcomputer in said first computer; selecting said second storage apparatusbased on said volume information using said first computer; requesting,from said first computer to said second computer via the communicationline, the reading of data stored in said second storage apparatus insaid fixed-length block format; reading, in response to said request,data in said fixed-length block format from said second storageapparatus using said second computer via said fixed length accessinterface and transferring said data to said first computer via saidcommunication line; converting, in said first computer, data in saidfixed-length block format to data in said variable-length block format;and transferring said data in said variable-length block format to saidbackup apparatus via said variable length access interface.
 2. A methodas described in claim 1, wherein said step for making said volumeinformation comprises a step for storing said volume information in apredetermined region formed in a main memory of said first computer. 3.A method as described in claim 1, wherein said volume information whichincludes information of a starting position and an ending position ofdata in said fixed-length block format in said second storage apparatus;and wherein said selecting step further comprises: getting a volumeserial number indicating an area in which data for backing up arestored; and checking whether said area is within a memory rangedetermined by said starting position and said ending position of data insaid second storage apparatus which is indicated by said volumeinformation, wherein said requesting step executed when the area iswithin the memory range of said second storage apparatus, by said firststorage apparatus.
 4. A method as described in claim 3, furthercomprising the steps of: reading data stored in said first storageapparatus when the area is not within the memory range of said secondstorage apparatus using said first computer.
 5. A method as described inclaim 4, wherein said second storage apparatus is connected to saidfirst computer via another fixed-length access interface, and methodfurther comprising the steps of: reading data stored in said secondstorage apparatus via said another fixed-length access interface whenthe area is within the memory range of said second storage apparatus. 6.A method as described in claim 5, further comprising the steps of:stopping execution of application of said second computer using saidsecond storage apparatus and unmounting a volume included in said secondstorage apparatus before execution of said making step; and mountingsaid volume and restarting said application after execution of saidtransferring step.
 7. A method as described in claim 6, wherein saidtransferring step is executed after collecting a certain amount of datasent from said second storage apparatus.
 8. In a computer systemincluding: a first computer; a second computer connected to said firstcomputer via a communication line; a first storage apparatus connectedto said first computer; a second storage apparatus connected to saidfirst computer via a fixed-length access interface and connected to saidsecond computer and storing data in a fixed-length block format used bysaid second computer; and a backup apparatus connected to said firstcomputer via a variable length access interface and storing data in avariable-length block format; a backup method for backing up data storedin said second storage apparatus to said backup apparatus comprising thesteps of: making volume information used to access data stored in saidsecond storage apparatus in said fixed-length block format from saidfirst computer in said first computer; selecting said second storageapparatus based on said volume information using said first computer;reading said data stored in said second storage apparatus in saidfixed-length block format from said second storage apparatus via saidfixed-length access interface using said first computer based oninformation contained in said volume information; converting, in saidfirst computer, said data in said fixed-length block format into data insaid variable-length block format; and transferring said converted datain said variable-length block format to said backup apparatus via saidvariable length access interface.
 9. A computer connected to backupapparatus storing data in a variable-length block format, comprising: afirst communication unit to communicate with another computer which isconnected to a second storage apparatus, a second communication unitusing a variable-length access interface connected to said backupapparatus and, a third communication unit connected to a first storageapparatus; a processor and; a memory, wherein said processor storesvolume information in said memory, selects said second storage apparatusfor accessing based on said volume information, requests said anothercomputer to send data stored in said second storage apparatus infixed-length block format through said first communication unit,receives said data from said another computer through said firstcommunication unit, converts said data to data in variable-length blockformat and transfers said converted data to said backup apparatusthrough said second communication unit.
 10. A computer as described inclaim 9, wherein said processor receives a volume serial number whichindicates an area in which data for backing up are stored, checkswhether said area is within a memory range of said second storageapparatus and requests said another computer to send said data throughsaid first communication unit when the area is within the memory rangeof said second storage apparatus.
 11. A computer as described in claim10, wherein said processor reads data stored in said first storageapparatus via said third communication unit when the area is not withinthe memory range of said second storage apparatus.
 12. A computer asdescribed in claim 11, further comprising a fourth communication unitusing a fixed-length access interface connected to a second storageapparatus, wherein said processor reads data stored in said secondstorage apparatus via said fourth communication unit when the area iswithin the memory range of said second storage apparatus.
 13. A systemcomprising: a first computer, a second computer connected to said firstcomputer through communication line, a backup apparatus connected tosaid first computer via a variable length access interface storing datain a variable-length block format; a first storage apparatus connectedto said first computer; and a second storage apparatus storing data in afixed-length block format connected to said second computer via afixed-length access interface, wherein said first computer makes volumeinformation, selects said second storage apparatus based on said volumeinformation, requests said second computer to send data stored in saidsecond storage apparatus, wherein said second computer reads said datastored in said second storage apparatus via said fixed-length accessinterface and transfers said data to said first computer via saidcommunication line based on said request, and wherein said firstcomputer receives said transferred data, converts said received data toa variable-length block format and transfers said converted data to saidbackup apparatus via said variable length access interface.
 14. A systemaccording to claim 13, wherein said, second storage apparatus connectedto said first computer via another fixed-length access interface,wherein said first computer reads data stored in said second storageapparatus from said second storage apparatus via said anotherfixed-length access interface when said first computer selects saidsecond storage apparatus by using said volume information.
 15. A systemaccording to claim 14, wherein said first computer generates theinformation to identify volume.